Nickel-titanium alloys are commonly used for the manufacture of intraluminal biomedical devices, such as self-expandable stents, stent grafts, embolic protection filters, and stone extraction baskets. Such devices may exploit the superelastic or shape memory behavior of equiatomic or near-equiatomic nickel-titanium alloys, which are commonly referred to as Nitinol.
As a result of the poor radiopacity of nickel-titanium alloys, however, such devices may be difficult to visualize from outside the body using non-invasive imaging techniques, such as x-ray fluoroscopy. Visualization is particularly problematic when the intraluminal device is made of fine wires or thin-walled struts. Consequently, a clinician may not be able to accurately place and/or manipulate a Nitinol stent or basket within a body vessel.
Current approaches to improving the radiopacity of nickel-titanium medical devices include the use of radiopaque markers or coatings. For example, gold markers attached to ends of a stent may guide the positioning of the device and delineate its length during an x-ray procedure. Alternatively, a medical device may be plated, clad or otherwise coated with gold or another heavy metal to create a radiopaque surface or outer layer. In another approach, a heavy metal cylinder may be included within the lumen of a stent to produce a radiopaque core. These approaches to improving radiopacity may have shortcomings, however. In some cases, markers may be easily dislodged or may undesirably increase the delivery profile of the device. A surface coating or cladding may delaminate as the medical device is expanded or it may interfere with the mechanical behavior of the device. Radiopaque cores may be expensive to fabricate. Galvanic corrosion may also be a problem. Furthermore, gold and other heavy metals, such as platinum, palladium, and tungsten, tend to be costly.